For many photonic applications such as high-capacity photonic switching, photonic transmitters and photonic receivers, it is necessary to couple light between optical fibers and a photonic chip. There are size limitations to the design of the coupler. A typical large size photonic chip may be in the scale of 25 mm by 25 mm. Single mode optical fibers produced commercially typically have a cladding diameter of 125 μm to 250 μm. In such a case, a maximum of 100-200 fibers can be arranged in a line across a photonic chip. To achieve a larger number count, such as 1000 fibers, a two-dimensional array of fibers may be required. Coupling an array of fibers to a photonic chip can be achieved using an array of optical couplers.
Light propagating in most optical fibers contains two orthogonal polarization components. Photonic chip circuits, however, often operate in a single polarization. One solution is to implement so called polarization diversity to perform the desired operations of the chip on two polarization components in parallel. For example, in a photonic switch with polarization diversity, the switching between inputs and outputs may be done by switching both components in an identical manner. As well, in a receiver for a polarization encoded signal, each component may need to be directed to a separate receiving circuit operating in a single polarization of light.
Accordingly, an apparatus is desired that can couple light between a fiber array and a photonic chip with polarization diversity.